Extrusion die

ABSTRACT

A continuous casting mold includes mold plates which enclose the casting cross section and in which cooling channels extend. The mold plates are connectable to a water box by screw elements which are formed by fastening bolts having a threaded shank which is screwable into fastening threads located in the mold plate. To achieve a uniform cooling in a continuous casting mold, the fastening threads are arranged such that their center longitudinal axes extend between two adjacent coolant channels of the plurality of cooling channels. The diameter of each threaded bore hole of the fastening threads is greater than the distance between the two adjacent cooling channels, and each bore hole of the fastening threads ends at a distance from the floor of the plurality of cooling channels to define the screw-in depth of the fastening bolts.

The invention is directed to a continuous casting mold with mold plateswhich enclose the casting cross section and in which cooling channelsextend. The mold plates are connected to a water box by screw elements,and the screw elements are formed by fastening bolts with a threadedshank which can be screwed into fastening threads in the mold plate.

With the exception of tubular molds for billets, molds for thecontinuous casting of steel comprise a plurality of mold plates, whichtogether form a cavity. The molten metal is poured into this cavity,partially solidifies, and is conducted downward. The format variesbetween slabs, thin slabs, blooms, or beam blanks depending on the shapeof this cavity.

The mold plates, which are fashioned almost exclusively from copperalloys, are acted upon by very high thermal and mechanical loads duringthe casting operation. The mold plates are fastened at the back to awater box so that the mold will retain its shape in spite of the forcesacting on it during casting. In particular, this should prevent largegaps from forming in the area of contact between the individual moldplates of a mold. Also, the cooling water of the mold may not be allowedto escape freely and come into contact with the molten steel.

Depending on the construction and dimensions of the molds, the moldplates are fastened to the water boxes at the back in different ways.Examples for the construction of the mold plates are disclosed in EP 1398 099 B1 and WO 02/07915.

Usually, bore holes having threads into which bolts or screws arescrewed are located on the back of the mold plates. To ensure a strengthsufficient to prevent the fastening elements from being torn out of thecopper, the fastening threads or threaded bore holes must besufficiently deep and have a sufficiently large diameter.

The dimensions, quantity and spacing of the threaded bore holes dependamong other things on the strength of the mold material, the dimensionsand shape of the mold plate and the loading during operation.

The back of the mold plates is needed not only for fastening purposesbut also for dissipating the extremely large amounts of heat releasedduring the solidification and cooling of steel.

Accordingly, cooling channels or cooling bore holes through which thecooling water is pumped at high pressure and velocity are located on theback of the molds.

For reasons relating to product quality and the lifetime of the moldplates that are used, it is necessary to ensure that cooling is asuniform as possible over the surface so that individual areas of thefront side of the mold do not have a substantially higher temperaturethan other areas immediately adjacent to them.

When the cooling water is conducted in the mold plate through coolingbore holes, the fastening threads can be located behind the coolingplane. However, producing drilled mold plates is relatively cumbersome,compared to mold plates with cut cooling channels. Further, the depth ofcut cooling channels and, therefore, the distance between the coolingchannels and the front side of the mold can be changed over the lengthand width of the mold plate and accordingly adapted to the occurringthermal loading.

WO 02/07915, cited above, discloses a mold arrangement in which coolantbore holes are provided parallel to one another in the copper plate. Thefastening bolts are arranged so that their center longitudinal axesextend in the center between two adjacent coolant bore holes.

In this construction, the distance between the outer walls of theadjacent coolant bore holes is greater than the outer diameter of thefastening bolt or threaded bore hole into which the shank of thefastening bolt is screwed. In this arrangement, the supporting threadedportion is located in the wall between the adjacent coolant bore holes.

In the prior art, fastening bore holes and cooling channels in moldswith cut cooling channels are located next to one another. Nevertheless,there are various possibilities for achieving the most uniform possiblecooling of the mold plate. Additional cooling bore holes can be locatedin front of the threaded bore holes in the direction of the flow of heator, rather than the cooling channels extending vertically over theheight of the mold plate, at least the next channels adjacent to the rowof fastening bore holes can pass around the fasteners at the smallestpossible distance (slalom slot).

It is the object of the invention to arrange and form the fastening boreholes and the cut cooling channels on the backs of mold plates in such away that a virtually uniform cooling is achieved.

This object is met according to the invention by a continuous castingmold with mold plates which enclose the casting cross section and inwhich cooling channels extend, the mold plates being connected to awater box by means of screw elements, and the screw elements are formedby fastening bolts with a threaded shank which can be screwed intofastening threads in the mold plate. The fastening threads are arrangedsuch that their center longitudinal axes extend between two adjacentcoolant channels in each instance, the diameter of each threaded borehole is greater than the distance between two adjacent cooling channels(4), and the bore holes for the fastening threads end at a distance fromthe floor of the cooling channels so as to define the screw-in depth ofthe fastening bolts.

Accordingly, the bore holes for the fastening threads are no longerlocated separately next to the cooling channels, but partially overlapthe cooling channels or are intersected by them.

The fastening bolts project somewhat into the cooling channels when theyare screwed into the fastening threads. However, the fastening bolts donot engage with the fastening threads in the area of the coolingchannels because there is no fastening thread in this area. On the otherhand, the fastening thread is also located in the wall areas of theadjacent cooling channels which face away from one another so that thetear-out strength is greater compared to fastening threads arranged inthe middle in cooling bore holes.

Tests have been conducted which show that it is possible to producethese fastening threads without difficulty, and the production does notdiffer from the production of fastening threads in solid material.Further, the fastening threads were examined to determine whether or notthey possess sufficient tear-out strength. The tests show that, underload, the channel threads have a tear-out strength comparable to that ofthreads in solid material. However, their diameter must be somewhatgreater compared to solid threads so that they have the same supportingsurface. By supporting surface is meant the supporting circumference xof the thread depth. The supporting circumference is the circumferenceof the thread minus the circular arcs that are cut out of the coolingchannels.

It is crucial that the cooling channels are deeper than the bore holesfor the fastening threads. In this way, there is cooling water below thethread (between the hot side of the mold and the base of the fasteningthreads), and there is accordingly also a cooling effect in thatlocation.

In order to ensure a uniform flow in the channels and to achieve higherflow rates, the channel cross section can be reduced above and/or belowand to the sides of the fastening threads by filler pieces. There willthen be islands remaining in the area of the fastenings for receivingthe thread inserts.

The invention will be described more fully in the following withreference to the drawings.

FIG. 1 is a schematic view of the arrangement and construction offastening threads in the back of a mold plate; and

FIG. 2 shows sections A-A and B-B from FIG. 1.

The mold plate is designated by 1 in FIG. 1. A known arrangement offastening threads, which has already been referred to above as slalomslots, is shown on the left-hand side.

The fastening threads 2 are enclosed, that is, surrounded in a slalomshape by the cooling channels 4.

In contrast, the fastening threads 3 shown in the center are arranged insuch a way that they are intersected by, or partially overlap, thecooling channels 4.

Naturally, there is no fastening thread in the area where the coolingchannels 4 intersect the bore holes 3, as can be seen from section A-Ain FIG. 2.

For the sake of comparison, FIG. 1 shows fastening threads 5 on theright-hand side which are located outside of the cooling channels andare accordingly situated in solid material. In order to achieve the sametear-out strength and the same supporting surfaces, they need only havea smaller diameter than the fastening threads intersected by the coolingchannels because there is no supporting fastening thread in the area ofthe cooling channels.

Section B-B in FIG. 2 shows a cross section through the solid materialof the mold, where the bore hole 3 is not intersected by the coolingchannel 4. The remaining fastening thread 2 is visible in the solidmaterial.

As is shown in section A-A in FIG. 2, the depth of the fastening threads2 and bore holes for these threads is smaller than the depth of thecooling channels 4 so that it is possible for coolant to flow throughthe cooling channel even when the fastening bolts are screwed in.

1.-3. (canceled)
 4. Continuous casting mold, comprising: a mold platewhich encloses a casting cross section and in which a plurality ofcooling channels extend, the mold plate being connectable to a water boxby screw elements formed from fastening bolts having a threaded shankwhich is screwable into first fastening threads located in said moldplate; wherein the first fastening threads are arranged such that theircenter longitudinal axes extend between two adjacent coolant channels ofsaid plural cooling channels, a diameter of each threaded bore hole ofthe first fastening threads is greater than a distance between the twoadjacent cooling channels, and each thread bore hole of the firstfastening threads ends at a distance from a floor of the plural coolingchannels so as to define a screw-in depth of the fastening bolts.
 5. Thecontinuous casting mold according to claim 4, wherein a diameter of thefirst fastening threads is greater than a diameter of second fasteningthreads arranged in a solid material portion of the mold plate so thatthe first and second fastening threads have a same supporting surface.6. The continuous casting mold according to claim 4, wherein a channelcross section of the cooling channels is reduced at least one of above,below and at sides of the first fastening threads by filler pieces toensure a uniform flow in each of said plural cooling channels and toachieve higher flow rates.
 7. The continuous casting mold according toclaim 5, wherein a channel cross section of the cooling channels isreduced at least one of above, below and at sides of the first fasteningthreads by filler pieces to ensure a uniform flow in each of said pluralcooling channels and to achieve higher flow rates.